This is a good question and there are several reasons for why it is important to review literature before identifying a research problem.
First, by reading literature on your topic first, you will get a sense of the work that has already been done. It is quite possible that your research problem has been overdone. There might be nothing more to say on that topic. In this case, you can move on.
Second, even if your project is new in a sense, your thoughts will become clearer as you look at the literature that is related to your topic. You can only benefit.
Third, no matter what you write on, there will be overlap with other research. Hence, the reading of literature will help your research in many ways. Also one of the greatest benefit of reading literature is that you can apply theories from other areas to your own project.
This is why most doctoral programs ask for a prospectus before they set you free to write your dissertation. In this prospectus, they want to know if you have looked at the field enough.
just because social research have scientific nature and research is based on previous work. in social research, this is most important to know about universe, their culture and language. review of literature confirm our way of research, methodology, what will we do? and what fault in previous researches.